The objective of this study is to evaluate the role of the lysosomal system and its complement of acid proteinases in the etiology of myocardial necrosis due to simulated ischemia. I have chosen to use isolated adult canine cardiac myocytes (cardiocytes) in this investigation of simulated ischemic injury in vitro (i.e., anoxia, acidosis and lack of available substrate) since, unlike whole myocardial tissue, measurement of thes variable factors in cardiocyte preparations is not hampered by the presence of different cell types, altered blood flow and difficulty in determining the precise areas of the tissue where injury is occurring. Since the lysosomal apparatus represents the only known intracellular proteolytic system capable of sequentlially degrading myofibrillar proteins completely to their constituent amino acids and since increases in lysosomal enzyme activities are found in many myopathies these enzymes are frequently implicated as a major factor in the muscle wasting process. By using the isolated adult cardiocyte model system, I plan to define the temporal relationship of the lysosomal system to the ischemic injury process. This study will include the use of control and anoxic/acidotic cells; analysis will be made of the cellular and subcellular distribution of acid hydrolases (primarily proteases), total and specific protein distribution (SDS-PAGE) and turnover (isotopic labeling), organelle integrity and function, and distribution of various nonlysosomal marker enzymes (e.g., CPK, succinate oxidation, cytochrome oxidase, etc.). It is hoped that these studies will lead to a better understanding of the etiology of myocardial necrosis and eventually to therapeutic approaches to ischemic injury.